1. Field of the Invention
The present invention relates to two-component epoxy resin and amine hardener compositions and, more particularly, to two-component compositions for sealing the circumferential joint between pairs of polymer-coated fiberglass fume duct sections with unsanded mating surfaces.
2. Description of the Related Art
Ductwork for corrosive vapor exhaust systems is used extensively in industries which utilize hazardous chemicals to process raw materials or perform manufacturing procedures. Such ductwork also is required in research and development laboratories which use highly reactive, toxic or otherwise hazardous chemicals in conducting experiments. Pat. No. 5,549,949 ("'949") is directed to sealant compositions for sealing the circumferential joint between pairs of dual-laminate fume duct sections, and to a joint sealing method which provides strong bonding between the sealant and phenolic/glass and vinyl ester surfaces without first preparing the mating surfaces by sanding them. As discussed therein, ducts are fabricated as sections which are transported to a job site and assembled there. Since a leak-proof joint is required between each pair of contiguous sections, even the smallest installation requires a considerable number of such joints. Because mechanical interfacing of section ends cannot by itself prevent leakage, a sealant must be applied circumferentially to each interface. The most time-consuming step in joining dual-laminate sections has been preparing the resin-impregnated surfaces to which the sealant must bond in order to effect a leak-proof seal. Unless the surfaces to be mated are sanded, the interposing sealant layer will not uniformly adhere to the surfaces, resulting in porosities in the hardened sealant through which fumes can leak. Joints must not only prevent fumes from escaping in day-to-day operation, but must also maintain integrity after prolonged exposure to corrosive or otherwise reactive chemicals. Also, joints must not fail catastrophically in the event a flame propagates through the ductwork or, if exposed directly to heat, become a source of smoke particulates or other contaminants.
Because of the wide diversity of chemicals used in industrial and research applications, it has been extremely difficult to provide a single material for fabricating ductwork which can withstand all the chemicals to which duct interiors may be exposed. Over the past forty years the trend in materials has been away from bare and coated metals and toward the use of plastics, particularly fiberglass reinforced plastics (FRP's) which incorporate various types of resins which provide desirable properties. U.S. Pat. No. 5,298,299 to L. E. Shea is directed to a dual-laminate tubular duct section having both good chemical resistance and good fire resistance. An inner laminate is formed by coating a mylar wrapped mandrel with a chemically resistant resin such as a halogenated vinyl ester and then wrapping the mandrel with successive layers of FRP fabric material saturated with the resin. An outer laminate is then formed directly over the inner laminate by applying successive layers of FRP fabric material saturated with a resorcinol or phenol/resorcinol type fire-retardant resin.
The three resin compositions disclosed in the '949 patent are mixtures of resins of several types, including epoxy novolac resin, aromatic epoxide resin and aliphatic trifunctional epoxy resin, to which is added a minor amount of glycidoxy silane. Both curing agent compositions include two types of cycloaliphatic amines and an aromatic tertiary amine, and one composition further includes a minor amount of amino silane. Adhesive shear strength tests were conducted for the resultant six sealant combinations to compare bonding of sanded vis-a-vis unsanded surfaces of phenolic resin-impregnated laminates and vinyl resin-impregnated dual-laminates. The test results identified one especially preferred sealant combination for phenolic laminates, and one especially preferred sealant combination for vinyl laminates. In both cases, the ratio of mean adhesive shear strength for unsanded compared to sanded surfaces was 0.97.
In contrast, the present invention is directed to two-component systems whose resin composition contains organic and inorganic filler materials, and whose curing agent composition is either totally a single type of amine, or the amine and a minor amount of amino silane.
Adding fillers to epoxy resin compositions to improve thixotropic and mechanical properties is well known. U.S. Pat. No. 5,665,797 to S. Tahara discloses epoxy resin compositions for sealing liquid crystal display cells which include at least one organic and/or inorganic filler. Suitable organic fillers include powders of polyethylene, polypropylene, polyvinylchloride, polystyrene, polyvinylacetate, polystyrene-polyvinylacetate copolymer, polymethacrylate, polyurethane, polyester, urea resin, phenol resin and epoxy resin. Suitable inorganic fillers include carbonates such as calcium carbonate and magneisum carbonate, sulfates such as barium sulfate and magnesium sulfate, silicates such as aluminum silicate and zirconium silicate, oxides such as iron oxide, titanium oxide, aluminum oxide (alumina), silicon oxide (silica) and zinc oxide, and kaolon, talc, asbestos powder, quartz powder, mica and glass fiber. U.S. Pat. No. 5,266,612 to W. G. Kim et al. provides an epoxy novolac resin composition for sealing semiconductor elements which includes an inorganic filler such as high purity fused silica micro-particles in an amount by weight of 65 to 85 percent. U.S. Pat. No. 3,996,175 to B. Schreiber et al. discloses epoxide resin molding materials whose composition contains organic and/or inorganic fillers. Suitable organic fillers include cellulose, polyamide, polyester and polyacrylonitrile fibers. Suitable inorganic fillers include quartz flour, ground shale, calcined kaolin, powdered chalk, wollastonite, mica, aluminum oxide trihydrate, diopside, ground dolomite, talcum, barium sulfate, graphite and wood flour.
Using a mixture of amines as the curing agent for epoxide resin compositions is well known in the art. U.S. Pat. No. 4,608,300 to U. Gruber teaches that impregnating a fiber composite with a curable, liquid, solvent-free epoxide resin matrix containing as the curing agent a specific mixture of amines based on monoamines results in a moderately viscous composition which fully cures at relatively low temperature, viz., below 120.degree. C. The matrix contains: (a) a liquid epoxide resin or a liquid mixture of epoxide resins; (b) an aliphatic or cycloaliphatic primary monoamine and/or a disecondary diamine; and (c) a tertiary amine which cures by catalysis or (d) a cycloaliphatic diamine or polyamine.
Combining epoxy resins and amino silanes is known. U.S. Pat. No. 5,173,206 to E. D. Dickens, Jr. et al. is directed to coating compositions which when applied to rare earth magnets reduce oxidiation and/or inhibit corrosion. The compositions are formed by combining (a) an amino silane and (b) either an epoxy silane and/or an epoxy resin.